Configuring VTP on Cisco Switches

VLAN Trunking Protocol, or just VTP, is a useful feature for managing VLANs across multiple switches. VTP replicates configured VLANs to all participating switches. You can say it’s more of a replication protocol and instead of a trunking protocol.

On that same note, VTP can take down your network if you’re not very careful. Why would VTP take down your network? Cisco switches can be configured in one of three VTP modes:

Server

Client

Transparent

Server mode is the default for Cisco switches. The switch in Server mode is where VLANs are configured.

Client mode grabs its VLAN configuration from the Server switch. It doesn’t actually place the VLANs in a vlan.dat file.

Switches in Transparent mode are rebels and don’t follow switches in Server or Client mode. If they receive VTP advertisements they will be kind and forward them along. In Transparent mode you can configure VLANs normally as you would on a Server switch.

VTP can be dangerous if a switch is deployed with a higher VTP revision number than the rest of the VTP switches. Because of that, switches in Client mode will download whatever VLAN configuration that switch has, potentially wiping out your current configuration. So when deploying switches, preconfigure them as Transparent mode. Or simply don’t use VTP.

Configuration

VTP Status

Before we begin configuring VTP it’s a good idea to display the current VTP configuration on each switch.

Switch 2 and 3 are missing VLANs 20 and 30. Once VTP is configured VLANs 20 and 30 will automatically be replicated to Switch 2 and 3.

Configure VTP

Now we get into the meat of the topic. We begin by configuring Switch 1 as the VTP server. I am then changing all the switches to my own domain name, using VTP version 2, and we will set a VTP password.

VTP actually takes a while to replicate the VLANs but to really get it going, all you have to do is configure a new VLAN on Switch 1. I will enable VTP debugging on SW1 and SW2 so we can see VTP in action.